For explaining more sufficiently the technical standards relating to the present invention at this point, the patents, the patent applications, the patent gazettes, and the scientific papers being cited or specified in the present application, are incorporated herein by reference in its entirely. In recent years, as markets for small or portable electronic devices such as a laptop personal computer and a cellular phone have been rapidly expanded, there have been increasing requirements for a small-weight and a large-capacity of the battery used in these devices. To satisfy the requirements, the secondary batteries are extensively being developed, which utilizes an electrochemical reaction associated with charge transfer on alkali-metal ions as a charge carrier, such as lithium ions. Among them, a lithium-ion secondary battery has been used in a variety of electronic devices as a large-capacity battery with an excellent stability and a higher energy density. Such a lithium-ion secondary battery uses a lithium-containing transition metal oxide, such as lithium manganese oxide and lithium cobalt oxide, in a positive electrode as active materials and a carbon in a negative electrode, and performs charge and discharge utilizing insertion and extraction reactions of lithium ions to these active materials. However, since this lithium-ion secondary battery uses a metal oxide with a large specific gravity particularly in a positive electrode, there's much room for improvement in the battery capacity per unit weight. There have been, therefore, attempts for developing a large-capacity battery using a lighter electrode material.
For example, according to the specifications of U.S. Pat. No. 4,833,048 and Japanese Patent No. 2,715,778, a battery using an organic compound having a disulfide bond in a positive electrode have been disclosed. It utilizes, as a principle of a battery, an electrochemical oxidation-reduction reaction associated with formation and dissociation of a disulfide bond. These batteries use electrode materials comprised of elements with a smaller specific gravity such as sulfur and carbon as main components. These materials are effective to some extent in providing a large-capacity battery with a higher energy density. However, the problem remains that the capacity is liable to decrease after repeating the charge and discharge cycle, due to a diffusion of active material to electrolyte solution, and that the efficiency in reformation of a dissociated bond is small.
On the other hand, as a battery utilizing an organic compound, a battery using a conductive polymer as an electrode material, has also been suggested. This is a battery whose principle is doping and undoping reactions of electrolyte ions on the conductive polymer. The doping reaction as used herein is a reaction of stabilizing excitons such as charged solitons and polarons generated by oxidation or reduction of a conductive polymer by counter ions. On the other hand, a undoping reaction as used herein refers to a reaction which is opposite to the above doping reaction and in which excitons stabilized by counter ions are electrochemically oxidized or reduced. According to the specification of U.S. Pat. No. 4,442,187, a battery using conductive polymer such as this as a positive electrode or negative electrode material is disclosed. This battery is comprised of elements with a smaller specific gravity such as carbon and nitrogen only. Its development as a large-capacity battery has been expected.
A conductive polymer, however, has a property that excitons generated by oxidation or reduction are delocalized over a wide region of π-electron conjugated system and interacted with each other. It results in a limitation to a concentration of excitons generated, and therefore, a capacity of a battery is restricted. Thus, a battery using a conductive polymer as an electrode material is effective to some extent in terms of weight reduction, but there's much room for improvement in terms of increase in a capacity.
As described above, there have been various proposals for a battery which does not use a transition metal containing active material, in an attempt to achieve a large-capacity battery. There have been, however, provided no stable batteries with a higher energy density and a large capacity yet.
As described above, in a lithium-ion battery using a transition metal oxide in a positive electrode, a specific gravity of the element is high that it has been theoretically difficult to prepare a battery with a larger capacity than that currently used. There have been various proposals for a battery which does not use a transition metal containing active material, in an attempt to achieve a large-capacity battery. There have been, however, provided no stable batteries with a higher energy density and a large capacity yet.